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With the Authors Comfiiments. 

UPON THE ELEOTKICAL EXPERIMENTS TO DETEinilNE 

THE LOCATIOiN OF THE BULLET 

IN THE BODY OF THE LATE PRESIDENT OAKFIELD : 

AND UPON 

A SUCCESSFUL FORM OF INDUCTION BALANCE 

FOR THE PAINLESS DETECTION OF METALLIC MASSES 

IN THE HUMAN BODY. 

» 

Bv Alexander Graham Bell, Ph. D . 



(A paper read before the American Association for the Aclvauccraeut of 
Science, at the Montreal meeting, Angnst, 1882.) 



WITH A N A P r E N 1) I X . 



FOE PRIVATE CIRCULATION. 



WASHINGTON, D. C. 
GIBSON BROTHERS, PRINTERS. 

t 1882. 



■™^"^^^"^r^^^~r^^"?^^^T 



2 M^^ 



<^\' 



■■{M" 



""^ 



^ 



UPON THE ELEOTKICAL EXPEIMMEATS TO DETERMINE 

THE EOOATION OF THE BULEET 
IN THE BODY OF THE EATE PBESIDENT (iAKFlELl); 



AND UPON 



A SUCCESSFUL FORI OF INDUCTION BALANCE 

FOR THE PAINLESS DETECTION OF METALLIC MASSES 

IN THE HUMAN BODY.' 

By Alexander Graham B k l l . 



(A pai)er read before the American Association for the Advancement of 
Science, at the Montreal meeting, Augnst, 1882.) 



The sulijet't of my present paper recalls a time of intense 
excitement and painful suspense. . The long, weary struggle 
with the untinielv death-wound — the prolonged suffei'ing borne 
so bravely and \\ell by the lamented President (Tartleld — 
must still be fresh in e^'ery recollection. The whole world 
watched by his l)ed-side, and hopes and fears tilled every pass- 
ing hour. No one could \'enture to predict the eitd so long as 
the position of the ])ullet remained uidcnown. Tlie liullet 
might become safely encysted, but, on the othei" hand, recovery 
might depend upon its extraction. Tiie search witli knife and 
probe among vital and sensitive tissues could nt»t be otherwise 
than painful and dangerous; and the thought naturally arose 
that science should be al)le to discover some less barbarous 
method of exploration. 

Among other ideas ^ the thought occurred that the bullet 
might produce some sensible effect in modifying the field of 

' A preliminary notice relating to this paper was published in the CotnpUs 
Rendun of the French Academy of Sciences, Oct. 'idth, 1881. 
^ See Ai)pendix, note 1. 



iii(hicti()ii (if a <-(iil Id-ouulit iieur the Ixxly of the President, and 
that the h)cality of the hiillet niig'ht thus be determined with- 
out dang-er to tlie patient and \\itliout pain ; for it is well known 
tluit iinhu^tion can he powerfully exerted thi-ough the human 
hodv without producing any sensation whatever. 

Upon tliC Indancnuj of IioJ ud'ioii. 

Tlie intluence that is exercised upon induction hy metallic 
masses has formed the sul)ject of numerous experiments by dif- 
ferent investigators; and the principle of lialancing the effects 
of induction on one portion of a circuit l)y ecpial and opposite 
effects pro(hiced upon anothei" portion lias l)een utilized in 
nearly all such investigations. 

The earliest form of induction l»alance for this purpose ap- 
pears to have been devised in Germany by Prof. Dove,' about 
tlie year 1841, and a good description of it in the English lan- 
guage may be found in I)e la Pive's "Treatise on Electricity,*" 
(1853 edition, vol. I, pp. 418-433)2. 

Another and superior arrangement for the same purpose is 
the well-known induction balance of Prof. 1). E. lluglies^. 

The Static Induction Balance of J. P]. II. Gordon^ though 
primarily intended foi* experiments upon specitic inductive ca- 
pacity, might also, j)erhaps, l)e employed in the same class of 
investigations. 

My own attenti(»n was directed to the balancing of iinhiction 
a immber of years ago by the disturbing noises prochu-ed in tlie 
telephone by the operation of telegra|)hic instininients upon 
lines running near the telephone conductor. 

The difficulty was remedied i)y using two conductors instead 
of one, and by so arranging them with reference to the disturb- 
ing wires that the currents induced in one of the telephone 
conductors were exactly equal and opposite to those induced in 

' Pdgg. Auu. vol. liv, pp. 305-335. 

- A .similar apj^iaratus was iudepeiideutly devised iu America a uiimber of 
years ago by Prof. Rowland, of Johns Hopkins University. It is to be re- 
gretted that his discovery of the fact that he had been anticipated by Dove 
prevented Prof. Rowland from comijleting and iinblishiug his i-esearches. 

3 Phil. Mag., July, 1879, vol. ii, p. .50. 

•* Phil. Trans, for 1879, p. 417, 



the other. In this way an inchiction l)ahuK;e was produecd 
and a quiet circuit secured fur telephonic purposes. This 
method was patented in England in November, 1877, and dur- 
ing the whole winter of 1877-8 I was engaged in London up(.n 
experiments relating to the subject. 

In the course of these researches I made frc(|ucnt use of Hat 
spirals of insulated wire, like those employed by the late Prof. 
Henry ^ in his experiments upon induction. 

My method was to pass a rapidly interrupted voltaic current 
through one tlat spii-al while I examined its field of inchiction 
by means of another tiat spiral connected with a telephone. 
The currents induced in the latter coil prochiced a musical 
tone from the telephone. 

At every point in the field of induction it was found that by 
turning the plane of the exploring coil a position of silence 
could l)e obtained, and another of maxinnnn sound, the two 
positions making a right angle with one another. 

It was also noticed that wlien a position of silence was estab- 
lished a piece of metal brought within tlie lield of induction 
caused the telephone to sound. This effect was most mai'ked 
when the two flat spirals were in close proximity, and were 
arranged with their planes parallel, as shown in Fig. 1. 

When a silver coin, such as a half-crown or florin, was passed 
across the face of tlie two coils, the silence of the telephone 
was broken thi-ee times. The instrument emitted a nnisical 
tone when the metallic disk passed the points marked 1, 2, and 




3 in the illustration, but the loudest effect was produced wlien 
the coin crossed the area marked "2," where the two coils 
overlapped. 

After my return to America I embodied these and other 
results in a paper " Ujjon Neio Methods of Iu'j)l(>riiitj the Field 

' Sillimau's Jouruul, xxviii, 329: xxxviii, 2(H): xli, 117. 



of huhidloit of Fhd Sj/lra/.s," which was read l)efore this 
association at the Suratog'a meeting!; in Ani2;nst, 1879. 

Pi'dct'ical Aj)j>Hc((f''(>ii. 

Whik' hr<»()(iini;- over the prohleni of the detection of the 
l)iinet ill the body of President Garliekl, these experiments 
made in p:n,i;-hind returned vividly to my mind. It seemed to 
me that if the overhipping area "2'' of the two coils shown in 
Fig. 1 could he l)rought over the seat of tlie luillet without 
disturhing the relative positicins of the coils, the telephone 
would pro])aJily announce the presence of tlie hidlet by an 
audible s<.)und. 

A crude experiment was at once made to test the idea. A 
large, single-pole electro-magnet (tlie coi-e of which was com- 
posed of a bundle of line iron wires) was used in place of coil 
A (Fig. 1 ;) and a small coil of line wire taken from a hand 
telephone was arranged a little to one side of the pole to rep- 
resent coil B. The small coil l)eing connected with a telephone, 
a l)attery current was passed through the coil of the electro' 
magnet, and the battery circuit was made and l)roken by an 
assistant. 

Under these circumstances a much better Italance was 
obtained than could possibly kave been anticipated. Upon now 
bringing a leaden bullet near the small coil, a distinct ticking 
sound could l)e heard from the telephone each time the Itattery 
circuit was made and Itroken. 

Beiuir absent from my laboratoi-y, and without facilities for 
proper experiment, I coimnunicated my ideas U) Mr. Charles 
Williams, Jr., of Boston, manufacturer of electrical and tele- 
phonic apparatus, who kindly placed the resources of his large 
establishment at my service ; and, at great personal inconve- 
nien(;e, delegated his best workmen to attend to my experiments. 
Upon attempting to devise an appropriate form of apparatus 
for the special purpose in view I saw tiu\t there were great 
practiciil dithculties in the way of utilizing the arrangement 
shown in Fig 1, and it occurred to me that the apparatus of 
Prof. Hughes might perhaps l)e employed with more advantage 
as the basis of my experiments. In the ordinary form of 



5 



Hughes' induction balance four coils are used, as shown in F'mx. 2. 
Through the agency of a Hughes microphone the tit-king of a 
cl'ock is made to create an electri<*al disturbance In the voltaic 




circuit contaimng the two primarv coils ( A C) and a corre- 
sponding disturbance is produced by induction in tlie two 
secondary coils (B D) connected with the telephone. If the 
connections are so arranged that the currents induced in the 
telephone circuit by the coils A C are in the same direction, 
the ticking of the clock is heard very plainly, liut if tliey are 
in opposite directions no sound is perceived. 

In the latter case the action of one primary coil (A) opposes 
that of the other, (C,) and an electrical balance results. If 
now a piece of metal is brought near one pair of coils (say A 
B) the l)alance is disturbed and the ticking of the clock is 
audible at the telephone. The arrangement of the coils (A, 
B, C, I)) was the point to be studied, the microphone attach- 
ment l)eing of no importance in the combination ; for it is well 
known tliat a rlieotome to 1 »reak tlie primary circuit c( )mpletely at 
intervals can l)e substituted for tlie microphone with advantage. 

It seemed to me that two of the coils (A B) in the Iluglies 
inducti(m l)alance might be attached rigidly to a wooden handle, 
so as to be moved over the seat of the l)ullet without changing 
their relative positions, and that all the adjnstments necessary 
might l)e made on the other pair of coils, which need not be 
moved from their place, and would not therefore l)e lial)le to 
disarrangement. If a single pair of coils were to be used as in 
Fig. 1, they must be adjustal)le one upon the otlier. But if dur- 
ing the course of exploration tlie coil 1> (Fig. 1) should lie 



< 



moved from its proper position even to the extent only of a 
small fraction of a millimetre, the l)alanee would be disturbed 
and the exploration might have to l)e stopped in order to ad- 
just the apparatus. These considerations led me to the concln- 
sion that some moditicatioii of the Hughes induction balance 
was most suitable for my purpose, and I innnediately com- 
menced tlie construction of such an apparatus. 

Jnst at this time I learned from the newspapers that Prof. 
Simon Newcoml*, of Washington, had the idea of nsing a mag- 
netic needle to indicate by retardation of its rotation the prox- 
imity of the l)ullet in the l)ody of the President, and I tele- 
graphed to Prof. Newcoml) the oifer -of my assistance in carry- 
ing on experiments, knowing the comparative ditticulty he 
would experience in having apparatus made in Washington. 

At his suggestion I tested the point whether the rotation of 
a leaden disk and of a leaden bullet miderneath a delicately sus- 
pended magnetic needle wonld cause a detlectiou of the needle. 

The disk occasioned a deflection, but the l)ullet produced no 
sensi])le effect. I telegraphed the result to Prof. Kewcomb, 
and at the same time took occasion to inform him of the hope- 
ful results I had olttained with the crudely constructed induc- 
tion balan<'e referi-ed to above. 

I was much gratified l»y his immediate appreciation of the ex- 
periment. He telegraphed that he thought an iuduction l)alance 
promised a unich more hopeful solution of the prol)lem than 
his own method, and encouraged me in ev^ery way to continue 
my expeiiments. 

This appreciation determined me to proceed to my laboi-utory 
at Washington, where I was accompanied by Mr. Sunnier 
Tainter, who was anxious to assist in such a cause. I learned 
from Prof. Newcomb that Mr. Geo. M. Hopkins, of Brook- 
^'*j lyii, had independently suggested the use of Hughes' induc- 

tion balance, and had ma<le experiments in Brooklyn, the i-esults 
of which were published in the New York Tribune on tlie 11th 
of July, 1881.1 Mr. J. Stanley Brown (private secretary of 

' See A2>i)eudix, uote 2. 



President Garfield) kindly handed to me the letters he liad re- 
ceived from Mr. Hopkins, ^ and also a Hughes induction bal- 
ance like that shown in Fig. 2, which Mi-. Hopkins had forwarded 
to the Executive Mansion for trial. 

This apparatus was at once tested in my laboratory, witli i-e- 
snlts slightly better than those I had obtained in Boston. 

My Boston apparatus did not give a greater hearing (Hs- 
tance than 3 cm., whereas with the Hopkins a])p;ii-atu> I could 
distinguish effects at a distance of 3.75 cm. 

Two of Mr. Hopkins" coils (A B, Fig. '2) were then fas- 
tened upon a wooden handle to form an exploring instrument, 
and the whole apparatus was arranged for innuecHate use in 
case of any necessity arising foi' an experiment upon the Pres- 
ident. [ set myself in connnnnication with Mr. Hopkins, and 
requested his assistance and co-operation, and in reply received 
through Private Secretary Brown the following account of 
further experiments : 

"(30 Ikying Place, Brooklyn, '/"/>/ 1<», 1881. 
" Mr. J. Stanley" Brown : 

" Dear Sir : I have made two new instruments on plans differ- 
" ing from that sent, l)ut tliey yield no better results. The first 
" consisted of ^^^ j 

" two ol)long 
"coils a r - 
" ranged at 
" right angles saem^ot^. 
" to eacli oth- 
" er, thus : 

"The outer coil being of coarse wire (No. 18) placed in the 
" primary circuit, the inner coil being of very fine wire (No. 
" 36) and connected with a telephone. The parallel curi-ents 
" traversing the wires neutralized each otlier, and no audible 
" effects are perceived in the telephone, but on presenting a 
" metallic body to the instrument upon a line bisecting the 
" angle betw^ee'n the coils the clicking in the telephone is heard. 

"Tliis instrument possesses only one advantage over that 
" sent, and that is that it requires no adjustment. 

' See Appeudix, notes I! ;ui(l 1. 




A 



8 

" The other inf^tnmient consists of two hirge coils of very 
" fine wire (No. ?)(i) pla(-ed upon opposite sides of a coil of 
" coarse wire, (No. 10,) the fine coil beiiiij: connected so that 
" the induced currents ncuti'alize each otlier, tlnis: 



Fig. 4,. 



Interrupter. 




" I am sorrv to l)e (il)liged to say of this as of tlie other, that 
" it is no more sensitive tiian the one sent. T(j produce the 
" best effects from tlie instrument which you have it will he 
" necessary to use all the battery power possilde without l»urn- 
" ing the coils, and two receiving telephones of the best con- 
" struction must be used. 

" As I stated in the fii'st instance, if the l)all is more than 
" two inches deep, I thiniv it cannot be located l\v tliis means. 

" If larger coils were used the instrument might l)e operative 
" at a greater distance, but the area indicated as containing the 
" ball would 1)6 so large that the result would be indefiinte and 
" without value. 

" Hoping that Prof. P)ell will be able to succeed, 1 remain, 
" Yours very truly, 

"(jrEo. M. Hopkins.'' 

Prof, Hughes of London, England, Prof. Trowbridge of 
Harvard College, Prof. Rowhuid of Johns Hopkins University, 
and other authorities were consulted l)y telegraph as to the l)est 
theoretical form of induction balance for the purpose i"e(|uired, 
wlnle empirical expei'iments were being carried on under my 
direction in my laboratory at Washington by Mr. Sunnier 
Tainter ; in the electrical work-shop of Davis and Watts, in 
Baltimore, by Mr. J. H. C. Watts, and in tlie estal)lishnient of 
Mr. Chas. Williams, Jr., in Boston, by Mr. Thomas A. Gleason. 
To test the influence of size of coil an instrument was con- 
structed in whicJi the coils were no larger than the bullet for 
which we sought, (as had been suggested by Prof. Kew(^onil),)^ 
and experiments were also made with the enorm<:)us coils used 
by the late Prof. Henry in his researches upon induction, whicli 

^ See Ai)pendix, uote 5. 



9 



To pTiniary coils oF 

^intiMcUon baUmce. 



were kindly lent to me for the purpose by the Smithsonian In- 
stitution, hut neither the small nor the larii;e coils produced moi'e 
satisfactory results tliaii those we had already obtained. 

To test battery power, 20 enormous Bunsen elements, which 
had formerly l)een used to light the gas at the (Japitol, were 
placed at my disposal l)y Mr. Rogers, electrician of the Capitol, 
l)ut while great electro-motive foi-ce was evidently of vise we 
dei'ived no advantage from such a battery as this. 

To test the influence of speed of interruption, Mr. Mai-ean, 
Supt. of the Western Union Telegraph Co. in \Va>liington, 
kindly lent ns an electric motor, l)y means of wlii(.-,h we were 
able, with the aid of a rotating connuutator, to obtain inter- 
ruptions of the primary circuit of all rates up to (">(>(> inten-up- 
tions per second, ^ and we 
found that the more rapid J't^o. 

the rate of interruption the 
UK )i'e distinct was the sound 
in the telephone. The 
hearing distance, however, 
was not proportionately 
increased. The automatic 
interrupter, (shown in Fig. 
5,) yielding aljout 100 in- 
terruptions per s e c o n d , 
gave as good results as any, 
and was much more conve- 
nient. This interrupter 
was therefore afterwards 
used exclusively in our ex- 
periments. 

The theoretical form of coil suggested by Pi-of. John Trow- 
bridge- was substantially the same as that proposed by Prof. 
Rowland,'' and is shown in Fig. 0. 

The ari'angement was quite sensitive to metal placed in the 

1 Mr. Sviiuner Tainter has since made au apparatus operating in a similar 
manner by means of which he has obtained as many as 4, ()()() interruptions of 
the circuit jjer second. 

2 See Appendix, note G. 
^ See Appendix, note 7. 




10 



inti'i-ior of the coil, l>ut the hearing distance for a l»nllet exter- 
nal to tlie coils was no o-reater than l)efore.^ 



J'^ig-. «}. 




Prof. Hughes ■-' proposed to have two flat superposed coils 
wound on a single reel, so that the two coils should form a sin- 
gle one as regards their relative distance ; and Mi-. F. T. Bick- 
ford, Washington correspondent of the New York Triltune, 
suggested winding two wires side hy side into a single coil, so 
that the relative distances of the wires from the hullet should 
be absolutely the same. Mr. Chas. E. Biiell-' and Dr. Chi- 
chester A. BelH proposed to determine the depth of the l)ullet 
beneath the surface l)y causing a similar bullet to appi'oach the 
l)alancing coils until silence was restored ; the secondary l)ullet 
it was presumed would then be at the same distance from the 
balancing coils as the embedded bullet from the exploring coils. 

The results of all the expei'iments so far made were unsatis- 
factory. I had ti-ied every thing that liad l)een suggested, but 
4 cm. i-emained the extreme limit of audibility for a bullet 
like that which had struck the President. Even when sucii a 
bullet was flattened l)y being flred against a board, and was 
presented with its flat side towards the ctoils of the explorer — 
the most favoi'able mode of pi'csentation — no l)cttcr I'esult was 
(d>taine(L 

' The balance ol)taiue(l was not qiiite perfect, and we have since discovered 
that the insulation of the wires of one of the secondary coils was defective. 
- See Api)endix, note 8. 
^ See Ajij^endix, note 9. 
^ See A2>2^endix. note 10. 



11 



(h'i(jinal ErpcniaenU. 

In the theoretical aiTangeuieiit reeoiiiineiKU'd l)y Pi'ofs. 
Trowhi'id^^^e and Rowland (Fijr. 6) the priniaiT coil A was of 
snialk^r diameter than the secondary B. This had ii'iven us no 
l)etter effects than the oi'dinary form of Hug-lies' balance, (see 
Fig. 2,) in which the two coils A B were of e(]ual diameter. 
We then ti'ied the effect of making the primai-y coil A of 
greater diameter than tlie „. ^ 

secondary B, (see Fig. 7,) 
and in this case we ap- 
peared to obtain an in- 
crease of heai'ing distance. 
Five centimetres (2 inch- 
es) was, howevei", the ut- 
most limit reached, when, 
on the l!»th of July, Mr. 
J. Stanley Brown and 
Dr. Wo(»dward visited my 
laboratory and witnessed 
some experiments. No difficulty was experienced in detecting 
a l)ullet held in tiie mouth l)y passing the expl(»ring coil over 
the cheek ; and the pi-esence of a fattened hullet held in the 
clenched band was also readily determined. Di'. Hliss, Dr. 
Heyburn, and Surgeon-General Barnes visited the laboratory 
next day and expressed themselves as very hopefully im])ressed 
by the experiments. These were suhsecjuently repeated in the 
sui'geon's room at the Executive Mansi(^n for tlie information 
of Dr. Fi'ank Hamilton and Dr. Agnew, who also seemed 
favorably im|)ressed. 

Such opinions from the surgeons in attendance upon the Presi- 
dent, and the continued interest shown hy Prof. Newcomb, 
encouraged me to proceed with the experiments.' 

It was now determined to test tlie effect of each coinolution 
of the primai'y coil, so as to arrive empirically at some idea (tf 

^I desire specially to exioress my grutitndf to Dr. Fruiik Iliuiiiltou for 
words of encouragement sjjoken at a later date when sympathy and cuconr- 
agement were greatly needed. 




L.ofC. 



13 

the best shape of coil. For this purpose Mr. Tainter con- 
structed the instruments shown in Fii;-. S. Circuhtr grooves were 
turned in two l)()ards, one of whicli is shown in perspective at 
A and the other in section at D. An insiihitcd copper wire 
could he pressed into any of these grooxcs so as to i;-ivo the 
wire an exactly circidai* sliape of known diameter, and the two 
ends were passed throuii'ii an orifice in the hack of the lioard, 
makin<^ connection with a similar ring of wire in the other in- 
strument as shown. A small secondary coil (B) of tine wire, 
which could he moveil with nuxk'rate friction ujton tlie lioi'i- 
zontal i'o(l, was coiiiiecteil to another similar coil, (E,j and to 
a telephone; and a small hrass rini-;, (C,) which could also he 
moved along the horizontal rod, ^vas used instead of a bullet 
to disturb the l»alance. 

In making an experiment with this apparatus the secondary 
coil (B) was first placed within the primary ring and in the 
same plane with it, and the balancing coil E was adjusted to 
produce silence. The l)rass ring C was then moved along the 
horiz(tntal rod until the l)alance was sensibly disturbed and the 
relative distances of the coils and the l)rass ring were ni»ted. 

Continuing the experiment the coil B was moved a tleter- 
mined distance beyond the plane of A, and the balancing coils 
again adjusted to silence. The l)i"ass ring C was once more 
caused todisturl) the l)alance, and the new hearing distance was 
noted. The following are tlie tabulated results of a series of 
experiments made on the 19th of July, 1881. The battery 
employed con>isted of six bichromate cells connected in series. 



14 



"o.S 
^05 


Distance Between — 




AB 

ill tit , 




B C 


AC 


mill. 


mill. 

17 


mm. 

17 




5 


14 


l'.» 


30 


10 


13 


23 




20 


9 


29 




30 


7 


37 




50 





50 







17 


17 




5 


19 


24 


50 


10 


26 


36 




20 


17 


37 




30 


14 


44 




50 


5 


55 







21 


21 




5 


23 


28 


81 


10 


23 


33 




20 


18 


38 




30 


14 


44 




50 


12 


62 







22 


22 




5 


25 


30 


113 


10 


27 


37 




20 


26 


46 




30 


26 


56 




50 


17 


67 



o c 


DiSTAN 


CE Betwhen — 


6 (5 








e ^ 














« 1 ^ 


A B 


BC 


AC 


mm. 


mm. 


mm. 


mm. 







27 


27 




5 


20 


25 


159 


10 


18 


28 




20 


17 


37 




30 


14 


44 




50 


14 


64 







12 


12 


1 


5 


18 


23 


206 


10 


25 


35 




20 


19 


39 




30 


22 


52 




50 


18 


68 







20 


20 




5 


18 


23 


253 


10 


20 


30 




20 


19 


39 




30 


23 


53 




50 


20 


70 



These li^'ures show that the distance from the primary coil 
A (Fii;'. 8) at irjiicji ffic influence of tlie J/v^s•,s• rimjC l>ec(tnie j^er- 
ceptihle increased inith the dianieter oftliepriniary ring, and th<d 
the secondM'y coil/Q req aired to he projected considerahiyheyond 
tJie plane of the printary in order to ohtain theniaximum effect. 

The conchisioii seemed a natural one that the degree of pro- 
jection A B of the secondary coil should proportionally 
increase with the diameter of the primary ring, but the tabu- 
lated tigures did not fully justify the inference. 

The experiments had necessarily occjupied a considerable 
time, and I thought that the difference between the results 
that should have V)een observed, according to the above hypoth- 
esis, and tliose that were actually obtained, might have been 
due to the gradual exhaustion of the ])ichromate battery em- 
ployed and t(» its polarization, altliough every care had l)een 
taken to preserve its power l)y removing the carbon and zinc 
plates from the solution, excepting when an observation was 



15 



made. To test whether the battery exerted any matei'ial intlu- 
ence upon the hearing- (U.staiice, a further series of experiments 
was made with the same hattery. 

It will be seen l)y reference to the tabulated statement shown 
above that the maxinuun hearing distance 13 C had been ob- 
tained with a primary ring 11.3 cm. in diameter when the dis- 
tance A B between the primary and secondary coils was one 
centimetre. This ari-angement of the apparatus was therefore 
adopted throughout the following experiments: 

Hearing distance 

1. Apparatus tried with 1 cell, (I'icliroiiiate V)attery)...(B C, Fig. 8) = 9 mm. 

2. Six cells iu series (BC. Fig. 8) =16 mm. 

3. Six cells iu multiple art- CBC,Fig.8)= 9 mm. 

4. Six cell iu two series of 3 each (BC, Fig.8) =15 mm. 

5. Same experimeut repeated (BC,rig.8) =13.5 mm. 

6. Same experimeut repeated by Mr. Taiuter (BC, Fig. 8; =12.5 mm. 

These experiments proved that battery power dhl exert an 
inlluence upon hearing distance, and also that the battery in 
use was gradually detei'iorating. 

I concluded, therefore, that if the battery powei- had re- 
mained constant, ^'>//- ^■ 

the hearmg distance J\ Secon/tuj-if i' 

might not only have 

Iteen proportional to 

the diameter of the ^r<^mmm^/- 

primary ring, Imt, in 

order to attain the ^-- -^'M 

maxinuun effect, the 
projection of the sec- 
ondary coil Ueyond 
the plane of the pri- 
mary might also have 
been found to in- 
crease in like pro- 
portion. 

This led me to try the effect of a conical primary coil A with 
the secondary B at its apex, as shown in Fig. 9, but the hear- 
ing distance for a bullet was only 8.5 cm. 




16 



Siuo-ulHi-ly ennng-h Mr. J. H. C. Watts, in Baltimore, had 
ndepeiidi'iitly arrived at a very similar form of coil, and with 

the instrument 



I^i^.lO. 




J"i0. Jl 



shown in Fig. Id 
he had obtained at 
one time a hearing- 
distance of 7.5 cm., 
(or 8 inches,') l)ut 
fi'om some cause 
not ascertained he 
was unable suhse- 
(juently tt) repro- 
duce the effect. 

The final form 
of apparatus adop- 
ted as tlie result of 
the al)ove experi- 
ments is sliown in F'ig. 11. With 
this arrangement and a bat- 
tery of six l)ichromate elements 
freshly set up, we were always 
sure of a liearing distance of at 
least 5 cm., although after the 
battery had l)een in use for s(tnie 
time the hearing distance hardly 
exceeded -t cm. 

Tlie following are tlie dimen- 
sions of the coils A B (Fig. 11) 
and tlieir resistance : 



Coil A External diixuieter 7 cm. 

luterual diameter 4.5 cm. 

Dej^th 2.4 cm. 

Wire used, No. 23, (cotton covered.) Kesistance, 2 ohms. 

Coil B External diameter 2.3 cm. 

Internal diameter cS mm. 

Deittli S mm. 

Wire used, No. 30, (silk covered.) Resistance, 75 ohms. 

1 See Ai>pendix, nt)te 11. 




17 

The face of the coil B projected l)ey(in(l tlie face <»f coil A 
4 mm. 

The balancing coils were made as nearly as ])ossilile the 
duplicates of A and B. The resistance of the coil oi' the tele- 
phone employed was 75 ohms. 

LiffiicDce of Baftenj Pover. 

The followino- experiments were made \\itli this apparatus 
(Fig. 11) on July 20th, 1881, to test the intluence of battery 
arrangements upon the hearing distance of a leaden bullet. 

I. Series of experimeiitK with a bichromate battery which ha'l previoudy been in 
use for a few minutes. 









Hearing distance of leaden 
bullet as observed by — 






A 


G. Bell. 


S. Tainter. 


1 cell 


2.4 
3.3 
3.7 
3.7 
4.0 
4.3 
2.(5 

3.8 
4.3 


cm. 
2 6 


2 cells ill series 


3J) 
4 1 


3 cells ill series 


4 cells iu series 


4 


5 cells iu series 


4 1 


* 
6 cells ill series 


4 4 


6 cells ill multiple arc 




2 9 


6 cells iu two series of 3 each 

(j cells iu three series of 2 eneh 


<> o 

o «> 
o o o 

4» O O 


— 


3.7 
4.0 



II. Sei'ies of experirnents with a Lealanche battery of twenty cells which Jrnd 
been set up for about one month. It had been kept normally upon open 
circuit, and had only been occasionally used. 

Hearing distance. 

20 cells iu series 3.3 cm. 

20 cells iu 10 series of 2 each 3.(5 cui. 

20 cells in 5 series of 4 each 4.1 cm. 

20 cells in 2 series of 10 each 3.0 cm. 

Although the battery appeared to be in good condition, a 
close inspection showed that the connections wt^-e dirty, and 
that one of the zinc wires was half hrokcii tliroiii;li. 



18 

The defective cell was now removed from the circuit, and 
the comioctions of all the other cells cleaned and tightened. 

III. 77tf fi'lloiring e.rperinientx were then made /r/'t/i the Leclniiehi cellx united 

in serien : 



No. of cells. 


Hearing dis- 
tance. 




cm. 


1 


2.7 


2 


2.8 


3 


3.0 


4 


3.3 


5 


3.3 


6 


3.5 


7 


3.6 


8 


3.8 


9 


4.0 


10 


3.8* 



No. of cells. 


Hearing dis- 
tance. 




cm. 


11 


3.8* 


12 


4.2 


13 


4.2 


14 


4.2 


15 


4.3 


in 


4.2 


17 


4.2 


18 


4.2 


19 


4.2 



These results are graphically represented in Fig. VI. 

It will be observed that the hearing distance was carried 
nearly one-third as far again as at first, simply by increasing 
the number of cells employed without any other change in the 
arrangement. It will also be noticed that tlie apparatus re- 
quires to l)e adjusted to complete silence in order to ol)tain the 
maximum effect. 

As a general result of all our experiments with voltaic bat- 
teries, we find that it is advis'ihtc to use a batter i/ possessing 
f/rer(t eledro-motive force and sl'tght internal resistance^ and to 
connect the cells in series. 

K-i'periniei}ts (ij>on Liriiuj Sul>jects. 

( )n the 'i2d of July an experiment was made at the recjuest 
of Dr. Bliss upon the person of Lieut. Simpson, wlio had car- 
ried a l)ullet in his l)ody for many years. 

When the exploring instrument (Fig. 11) was passed over 
the lieutenant's l)ack a sonorous spot was found, l)ut the indi- 
cations were too feeble to be implicitly relied upon. Imaii,'ina- 
tion very easily conjures up a feeble sound like that observe4, 



* Balance uot quite perfect. 



^ 




19 



20 



hut a uunilier of experinieiits l»y (liferent 'observers seemed to 
indicate that in this case there was an external cause for the 
sound — probably the presence of a very deeply-seated bullet. 
The results of this experiment were connnunicated to Dr. Bliss 
in a letter dated July 23d, 1881. i 

On the 25tli of July Prof. Kowland visited me at Washing- 
ton, and sug<^ested the use of a condenser in the primary cir- 
cuit. I had previously discussed this idea with Mr. Taintcr, 
l)ut, not having- a condenser at hand, we had been unable to make 
any experiment. Aftei- our conversation with Prof. Rowland, 
lu»wever, we weie so impi-essed by tlie importance of the point 
that we ol)tained a condenser next morning, and found it to pro- 
(hu-e not only a different (piality of sound when the bullet ap- 
proached the coils, but also to increase tlie hearing distance of 
the instrument shown in Fig. 11 at least one centimetre. 

On the evening of the same day (July 2(ith) our apparatus 
was carried to the Executive Mansion, and an experiment made 
upon the person of the President.- 

From some cause tlien unknown a l)alance could not be ob- 
tained, and the results were tlierefore uncertain and indetinite. 
It was discovered afterwards tliat a mistake liad been made in 
tlie mode of connecting the condenser. The latter sliould have 
been connected at E F, (Fig. 13,) whereas it was placed at E 
(i, tlius intlnen(;ing only one, instead of both, of the primai-y 
coils. 

With the condenser properly arranged experiments were 
tried on July 29 and oO on three soldiers from' the Soldiers' 
Home who had been wounded during the civil war, namely, 
John Teahan, Asa Head, and John McGill. 

In the case of John Teahan no results were obtained, hi 
the case of Asa Head, who had a buckshot in the idieek, loud 
and well-marked sounds were heard in the telephone ; and in 
the case of John McGill, who was supposed to carry a bullet 
in his back, no results were obtained. 

Further eff(»rts were then prosecuted for the improvement 
of the apparatus. 

1 See AiJjteudix, uote 12. 
^ See Api)endix, note 13. 



Os) 



Fiirfher E-rperunents to Iinprore Aj)j)rn'f(/u.s: 

Oni- attention had liitlierto Ueeu dii'ec-ted cliietiy to modiii- 
cations of the exploring instrnmeiit. We now investigated the 
effect, upon the hearing distance, of the coils used to obtain a 
l)alance. 

The following experiments, made July 29, 1881, hear upon 

the point : 

:Fip.ia. 




Exp. 1. (See Fig. 1-1.) Resistance of primary A of ex- 
ploring instrument, 2 ohms ; resistance of primary C of bal- 
ancing coils, also 2 ohms; resistance of exploring secondary B, 
140 ohms; and of l)alancing secondary D, 120 ohms. 

Result : Hearing distance of l)ullet from explorer A B, 3.5 
cm. Hearing distance from balancing coils C I), also 3.5 cm. 

Exp. 2. (See Fig. 15.) Same exploring coils as in Exp. 1, 
l)ut Ijalancing coils consisted of a flat primary, E — resistance, 
5.30 ohms ; and flat secondary, F — resistance, 83 ohms. The 
adjustment was made l)y sliding the se(;ondary coil ujion the 
primary until a position of silence was obtained. 

Result : Hearing distance from explorer A B, 1.5 cm. Hear- 
ing distance from E F, 3 cm. 

As a genei'al result of our experiments we found that irery 



23 

increase in the residduee of the fxiUuicuKj coils [especial hj the 
priiiKiry) rednced the hejii'iixj distunce of the exploriiuj instni- 




meat, and it became therefore <le8iral)le to do away with this 
source of i-esistance as inucli as possible. 

lietdi'n to Original Foi'ni of Apparatus. 

This led us l)ack to the original form of a]i]>ai-atus that 
had iirst occurred to me, (see Fig. 1,) in which a single 
pair of coils was employed. A few otlier experiments, made 
July 29, 1881, will show the importance of tlie point attained. 

Exp. 3. The two Hat coils E F used in experiment 2 were 
arranged as in Fig. 16, so as to form a balance by themselves. 

Result : Hearing distance, 1 caw. 

In all these experiments the l)attery used consisted of four 
cells, (Leclanchc.) 




Exp. 4. The same coils used in Exp. 3 were tried again, as 
shown in FiiT. 16, but with a l)attei-y of eight cells, (Leclanclic.) 



24 

Result: Hearing- distance, 8.7 cm., or nearly 3^ inches — a 
result quite unprecedented in our experiments. 

The following are tlie dimensions of the (;oils E F : 

Coil E Exterual (liuineter 10 cm. 

luteruiil (liaineter 2.5cm. 

Depth 1 cm. 

Wire used. No. 23, (silk-covered.) 

Coil F Exterual diameter 10 cm. 

Internal diameter 2.5 cm. 

Depth 1 cm. 

Wire used. No. 28, (silk-covered.) 




Exp. 5. The same coils E F, used in Exps. 2, 3, and 4, were 
tried once more with a battery of six large bichromate elements, 
and with a condenser, G, in the primary circuit as shown in 
Fig. 17. 

Result: Hearing distance 13 cm., or more than 5 in(;hes. 

This great increase in hearing distance seemed to l)e chiefly 
due to the condenser, for upon discoimecting it the hearing dis- 
tance was little more than 9 cm., but fm-ther experiments pr(n-ed 
that other causes also contributed to the result. 

Exp. 6. When the condenser was in circuit and the leaden 
l)ullet close to the coils (arranged as in Fig. 17) the sound pro- 
duced by the telephone was a musical note whose pitch was 
the same as that normally produced by the vibration of the 
reed of the interrupter. Mingled with this tone could be dis- 
tinguished a numl)er of feel)ler tones of very much higher 
pitch. Upon withdrawing the bullet gradually from the coils 
the fundamental sound Itecame fainter, and one of the high 
upper-partial tones gradually acquired pi'ominence ; and at a 
distance of about 8 or 9 cm. the fundamental could no longer 
be distinguished, but the high tone persisted, and was clearly 
audible up to a distance of 13 cm. The effect was very strik- 
iiiil, and when the hidlct was moved to and fro parallel to the 



25 

plane of the coils E F at a distance of about 10 cm., the tel- 
ephone emitted a shrill wliistling sound each time the sensitive 
area (H) was passed. 

It was noticed that other metals, such as inm, hrass, and 
copper, did not seem to reinforce tliis hig-h tone to anv great 
extent, hut l)rought out the fundainental at every distance where 
an effect was produced. 

Exp. 7. The condenser G (Fig. 17) was removed from the 
circuit and the leaden hullet held al)out 4 or 5 cm. from the 
coils E F. The fundamental tone was heard, and the charac- 
teristic upper-partial could also l)e distinguished, hut it was 
only faintly audible. Upon now suddenly replacing tlie con- 
denser the high upper-partial tone was instantly reinforced as 
if by a resonator. 

Exp. 8. The rheotome employed to interrupt the primary 
circuit (which had been placed in a distant room) was found 
to be vilu-ating badly. The reed I of the instrument (see also 
Fig. 5) was rattling against its contact pieces, thus producing 
an impure sound, and I could distinguish amongst the upper- 
partials the tone that had l)een reinforced l)y the condenser. 
Upon screwing up the contact pieces so as to improve tlie \i- 
bration I could no longer distinguish the particular upper-par- 
tial referred to, and upon returning to the room in wdiich the 
coils E F (Fig. 17) ^vere placed I could no longer detect tlie 
effects noted above in Exps. 6 and 7, and the hearing distance 
did not exceed 9 cm. 

TJte j^eculiar ejfecfs ohtahied tritJi ilte a ri'<iii<jeiiieitt xlunrn in 
Fig. 17 thus seemed to depend (1) upon <i particular kind of 
vihration of the reed o^ the interrupter^ prod i wing a certain high 
upper-partial or overtone, (2) up)on the nse of a condenser act- 
ing as a, sort of electrical resonator for this tone, and (8) upDn 
the use of the metal lead. 

Mr. Marean, of Washington, kindly lent mc a mnnber of 
condensers used by the Western Union Telegraph t-o., and we 
found, upon comiecting them with the coils E F, as shown in 
Fig. 17, and, holding a leaden bullet near the coils, that each con- 
denser reinforced a high upper-partial of different pitcli. ^\'e 
arrauii'ed \\\q, condensers so that thc\- could be s.iccessivelv in- 



26 

trodiiced into the circuit with great rapidity. The effect was 
very curious, and sounded somewhat like a Scotcli air phiyed 
upon the bag-pipes. The low Innn of the fundamental could 
1)0 heard cdutinuously, like the drone of the bag-pipe, while 
the highei- tone changed its pitch with each change of con- 
denser. 

The j)//c/i (>f ihi' liKjh tone rehtfoi'ved seenicil to dej^end 
upon the eledro-datic cdpaatu of tlie condenser employed^ but 
the exact relation between the two has not been ascertained. 
In experiments 5, 6, 7, 8, and the subsecpicnt experiments de- 
scribed above, the battery employed consisted of six pairs of 
carbon and zinc plates of large area placed in a solution of bi- 
chromate of potash containing sulphuric acid. 

The effects noted above were not produced satisfactorily 
when the battery was much run down, nor were they obtained 
with a Leclanche battery which had been set up for some time, 
but which appeared to be in good condition. 

It h evidently uecesmry in order to produce this cJinracter- 
istic high tone to use a Indtery possessiny conslderaUe electro- 
motive force cind slight internal resistance. 

Our experiments had reached this stage when, on Saturday, 
the 30th of July, 1881, I was requested to make another trial 
upon the person of the President at the evening dressing of the 
wound. 

At this time, however, we had no exploring instruments 
completed excepting one or two like that shown in Fig. 11 ; 
for it will be understood that the promising results noted al)Ove 
had been obtained from coils that were simply placed upon a 
tal)le and adjusted by hand. 

We immediately proceeded to the Executive Mansion with 
the apparatus shown in Fig. 13, prepared to make a trial, if it 
was deemed advisable; but upon learning of the results of our 
later experiments the surgeons resolved to postpone any further 
trial until we could arrange the coils (Fig. 17) in a portable 
form. 

Bv forced exertions the coils were arranged that same night 
in a wooden case, as shown in Fig. 18. This case consisted es- 
sentiallv of two oldoUir l)locks xV B. A shallow cii'culiir recess 




a 

o ^ 



? 




r, 


■p 


(D 




Q 


» 


M 


bo 


<D 


3 


•d 


<; 


a 


•^ 









(i) 


<i> 


tfl 




1, 




OS 

C5 




+3 


a 


C 




a; 


■d 


•c 


(D 


rn 


m 


0) 


3 




m 


Oh 


3 


0) 






rt 


crt 






03 


® 


a 


J3 


< 





28 

was turned out in eacli l)lo('k for tlie reception of one of the 
coils, and the two hhjcks were held together by four pins of 
el)onite, C, D, E, F, which passed np through slots in the upper 
block and were secured hy el)onite thumb-screws. 

When the instrument was completed I found to mj great 
distress that a balance could not l)e obtained by any adjust- 
ment of the apparatus. There was a position of mininjum 
sound, and the telephone responded to a bullet presented to tlie 
central part G of the instrument; but the hearing distance did 
not exceed 3 or -i cm., whereas we had obtained with the same 
coils l)efore the construction of the wooden case a perfect bal- 
ance and a hearing distance of 13 cm. 

After numerous unsuccessful experiments had been made to 
ascertain the cause of the difficulty it occui-red to me that if 
two adjoining convolutions in one of the coils, made contact 
at any point, a circuit of low resistance would be formed, (a 
single ring of wire, in fact,) in whicli the indriced curi'ents 
might circulate without reaching the telephone connected with 
the apparatus. I had previously measured the resistance of the 
coils without discovering any defect, Imt wlien I considered the 
large nnnd)er of convolutions in each coil it seemed possible 
that a defect of this kind might exist which could not be dis- 
covered l>y a Wheatstone Bridge, excepting by very delicate 
and accurate ol)servations. To test whether a short-circuited 
convoluiion would produce effects analagous to those observed, 
a piece of copper wire was bent into an annular form and the 
ends connected together. On ])ringing this metallic ring near 
a pair of coils, (A, B, Fig. 19,) properly adjusted to silence, the 
balance was loudly disturbed. The copper ring (C) was held 
as shown in Fig. 19, and the balance could not then l)e re- 
stored by any adjustment of the coils. A position of mininnnn 
sound was all that could l)e olttainetl, and the hearing distance 
was enormously reduced. This was^;/'///^// facie eviden(;e of the 
nature of the defect. 

The coils (Fig. 18) were then removed from their case, but 
a cursory examinati<ui revealed no defect. Upon trial, how- 
ever, (being arranged, as formerly, in Fig. 17,) a l»alance could 
not be obtained, and the hea]-ing distance was only about -1 



29 

cm. The defect was thus (lelinitclv IncatiMl in the coils tliciii- 
selves. 




Upon close examination it was noticed tliat the outside con- 
vohitions of tlie pi-imary coil were sliglitlj frayed at one part, 
hut it appeared hai'dly possihle that so 2;reat a defect could lie 
due to so apparently slight a cause. However, to test the mat- 
ter, I removed the outside layer of wires and then tested the 
coils again. 

Result : The defect had vanished — a perfect halance M'as oh- 
tained, and the liearing distance was again lo cm.' 

The coils were then replaced in theii' case and the (-ompleted 
instrument tested. The lower wooden block B (Fig. 18) was 

1 These experiiii_-uts hxve revealed the cause of the exti'eiue difficuUy always 
exiDerienced in obtaiuiug a perfect balance with coils of tine wire. I have 
recently used an Induction Balance to test the coudititm of the helices that 
were emijloyed in these researches, and have discovered that in a large per- 
centage of cases the insulation was defective. It is isossible that some of the 
results described in this paper (especially of the earlier experiments) maj' 
have been vitiated by errors due to defects in the coils that w^ere not sus- 
pected at the time. A defect of insulation that is quite immaterial for ordi- 
nary purposes maybe absolutely fatal to the success of an Induction Balance. 
Indeed, so unich care is recpiired in this respect that it is oxtremely difficult 
to obtain coils that are 2>erfectly suitable for an a]i])aratns intended to search 



30 

iuljiisted l>y hand as nearly as possible to the position of silence, 
and then the thnmh-screws C, D, E, F were tightened. 

The halance now ol)tained was not (juite perfect, hut hj 
8ti-ikin_i>- the lower l.lock 1> a few smart Idows witli a wooden 
mallet we were able ti> reduce the arrangement to complete 
silence. 

The instrument was then in such a sensitive con<Htion that 
it could scarcely I)e moved without affecting the halance. Upon 
gently swaying it backwards and forwards a pulsation of sound 
was heard at every swing. 

A¥hen the motion was carefully made, so that it was always 
in the same plane, no pulsations wei-e observed. They only 
occurred when the inclination of the coils was changed. 

This defect was found to be due to the bulging of the thin 
portion Ct of the wooden case (Fig. 18) under the weight of 
the enclosed coil, and the simple pressure of a finger on this 
portion of the case disturbed the !)alance. The movement of 
the lower coil when the instrument was swayed about must 
have l)een inconceivably small, but on account of the extreme 
sensitiveness of the arrangement it procku-ed a perceptil)le 
effect upon the balance. 

The pidsating sound did not seem to interfere with the de- 
tection of a bullet held in the clenched hand, nor did it seem 
to affect the hearing distance. I therefore despatched a mes- 

out a bullet imbedded iu the body. I nnw uwike it a rule to test every helix 
used iu luductiou Balauce experiments by briugiug it up to a system of bal- 
anced coils like that shown iu Fig. 17. 

1. If the helix is perfect the balauce is not disturl)ed uutil the terminals of 
the coil are connected. 

2. If there is a break in any of the convolutions the balance is not disturbed, 
even wheu the terminals are connected. 

3. If a convolution is short-circuited the balance is disturbed, even though 
the terminals are not connected, and the sound prodiiced is the fundamental 
of the rheotome employed to interrupt the primary circuit. 

4. If the insulation is defective the balance is disturbed, although the ter- 
minals are not connected, and a peciiliar sphittering effect is noticed like that 
produced by a series of sjiarks. 

I propose to apply this method practically as a means of testing the condi- 
tion of the helices \ised in the construction of Induction Coils and those em- 
ployed in the manufacture of telephones. 



31 

senger to the Executive Mansion, (StiiK lav iijoi-iiiii-;-, Julv ;>lsf,) 
with a note for JJr. Bliss, ' to let him know that the instnunent 
was in a condition to he used, should any neccssitv arise for 
an iiiunediate expentnent. At the same time I informed liim 
that the apparatus in its present form was very crudelv con- 
structed, and that I ho])ed to improve it very gi-eatlv in the 
course of a few da,ys. On Sunday afternoi.n (duly :Ust) we 
sent to the Soldiers' Home for Jolui McCiill, upon whom we 
had experimented the previous day without results, (using the 
apparatus shown in Fig 11.) 

Upon trying the new instrument (Fig. 18) we had no ditK- 
culty in finding a sonorous spot in his l)ack, at the place where 
the hidlet was always supposed to be. 

This result was at once comnnmicated to Dr. Bliss, =^ and in 
replj' we were recjuested to make the experiment upon the 
person of the President next morning. 

On Monday morning (Angust 1st, 1881) we accordingly re- 
moved our apparatus to the Executive Mansion. 

The Lute President (rdrffe/d. 

During the former experiment (July 26) a sudden sono- 
rous effect had been ()l)served upon passing a point near the 
spot where tho surgCDUs suspected tlie bullet to be lodged, 
l)ut 1 had been unable to verify this by a second observa- 
tion, although the exploring instrument (A B, Fig. i;>) was 
repeatedly passed ovei' the same place. The sound had been 
so loud and well marked that I believe<l at tlu^ time it nnist 
have been caused l)y a sudden irregulnrity in the viliration 
of the reed of the rheotome used to interrupt the primary 
circuit, foi" the arrangement (as explained above, p. 20) was 
not perfectly balanced, and any irregularity of this kind 
would, under these circumstances, have affected the tele- 
phone. At the same time the coincidence was remarkable 
that the exploring instrument should have been at that very 
time so near the suspected seat of the ball, and tins led to 
the thought that perhaps after all the bullet had been the 

' See Appendix, uote 15. 
^ See Appendix, uote 14. 



32 

cause of the sound. I felt coniident that the new instru- 
ment (Fig. 18) would at once decide the- question, for the ex- 
treme hearing distance of tlie former apparatus (Fig. lo) was 
only «> cm., and the apparatus shown in Fig. 18 was so supe- 
rior in this respect that if the sound had really been due to the 
bullet we should obtain with the new instrument distinct and 
well-marked effects. When the new explorer (Fig. 18) was 
passed over the suspected spot nothing was heard excepting a 
sliglit pulsatijig sound as the instrument was moved to and fro. 
This was evidence to me that the former sound had been of ac- 
cidental origin, whether tlie l)ullet was there or not. Witli the 
view of eliminating any erroi- of ol)servation caused by tlie 
pulsations due simply to the movement of the instrument, 1 
lifted the latter (without changing tlie inclination of the coils) 
to a height of about 50 centimetres above the body of the Pres- 
ident, and moved it to and fro in as nearly as possible the same 
way I had done at the lower elevation. 

I presumed that if the pulsations heard were due simply to 
the movement of the instrument, they should occur with equal 
strength at the two elevations ; but if any portion of the sonor- 
ous effect was due to the intluence of the Inillet, the pulsations 
at the two elevations would be different in intensity. I was 
struck by the fact that, although the sonorous pulsations were 
very feeble, they were sensibly louder when the instrument 
was close to the surface of the body than when it was raised. 
Continuing the exploration, I found a considoable area ov.er 
whicli similar effects were noticed, but upon carrying the in- 
strument towards the l)ack of the President, the difference be- 
tween the pulsations producted at the two elevations grew less 
and less, and finally could not be distinguished. 

The difference in the loudness of the sound at the two ele- 
vations was so slight that it prol)ably woidd not have been no- 
ticed by an ear unaccustomed to listen to feeble effects, and I 
feared that the general expectation tliat the l>ullet would be 
forind in that part of the body might have led me to imagine 
a difference that did not exist. For the purpose of eliminating 
as far as possible any personal error, I reipiested Mr. Sumner 
Tainter (wh > was the only other person present wlujse ear had 
been sufficiently trailed to be reliable in such an emergency) 



to repeat the experiment^; and let nie know tlic roiilt. I']."'! 
our i-eturn to my laboratory we eonipared notes, and I tound 
that his observations tallied with nnne. He deelared he coidd 
not o1)tain a distinctly localized effect, hnt stated tliat he had 
observed a reinforcement of the pulsation over an area of at least 
two inches in the neiu'hliorhood of tlie spot to wln'ch liis atten- 
tion liad primarily been directed, and that he was convinced 
that the bnllet was within that area. 

It appeared reasonably certain that the area of feeble sound 
was due to some external cause, and w^as not simply an ejfect 
of expectancy. In the al)sence of any other apparent cause 
for the phenomenon I was forced to agree in the conclusiou 
that it was due to the presence of tlie bnllet, and I so stated in 
mv report to the surwons.' I was l)v no means satisfied 
however, with the results ol)tained, for no such effects had been 
o])served before in our experiments with bullets. I tried to 
reproduce the effects by moving the instrument (Fig. 18) at 
different distances over a bullet, l)ut in every case where an 
effect was produced the sound was quite sharply localized. I 
thought that perhaps the body of the patient might have af- 
fected the result, and so experimented upon a I)ullet l)uried in a 
piece of meat, but no difference of effect was noted. This led 
me to fear that the extensive area of feeble sound might have 
l>een due to some extensive area of metal that ^vas imsuspected 
at the time, and I proceeded to the Executive Mansion next 
iiMrning (August '2) to ascertain from the surgeons Avhether 
tliey were perfectly sure that all metal had been removed fi-om 
the neighborhood of the l)ed. It was then recollected that 
underneath the horse-hair mattress on which the President lav 
was another mattress composed of steel wires. 

Upon ol»taining a duplicate, the mattress was found to con- 
sist of a sort of net of woven steel wires, with large meshes. 
The extent of the sonorous area having been so small, as com- 
pared with the area of the l)eTi, it seemed reasonal)le to con- 
clude that the steel mattress liad produced no detrimental effect. - 

' 8ee Ajjpeudix, note 10. 

- The death of Presideut (xaifield and the subseciiient poxt-itiorUin exani- 
inatiou. however, proved that the bullet was at too great a distance from the 
surface to have affected our api)aratns. 



34 

I was unable to continue experiments witii the steel mattress, as 
just at this time I was obliged to leave Washington on account 
of illness in my family. A.lthough I was unable for a long 
time afterwards to carry on personally Liu luetic )n Balance ex- 
periments, the inv^estigations were ably continued under my 
direction by Mr. Thomas Gleason, in the establishment of Mr. 
Charles Williams, Jr., in Boston. 

K.pperhneidi< (\tnt'u\nt'<l in Bnxfon. 

Mr. Tainter forwarded from Washington drawings of an 
improved apparatus he had designed to remedy the defects of 
the instrument shown in Fig. 18, in which the case, adjusting- 
screws, &c., were all to be composed of ebonite. 

Mr. Gleason constructed for me a number of siu-h ebonite in- 
struments differing slightly from one another in detail, and the 
appai-atus shown in Fig. 20 combined the different points that 
had l)een approved. 

The two coils A B were eccentrically arranged in two cir- 
cular disks of e!)onite, C D, and the adjustment was obtained 
by means of an el»onite key O, like the key used for tuning 
pianos, which turned a cam M pivoted in the u])per disk and 
working in a slot N in the lower disk. 

In order to prevent any movement of the coils, excepting 
that produced by the adjusting-key O, each coil was placed in 
a recess tiirned out in its ebonite disk, the edges of which were 
bevelled as shown at R. Parathne was then pom-ed in so as 
to till up each recess. But this alone did not prevent a 
sl'ght pulsation of sound when the instrument was swayed from 
side to side, and a very slight pressure of the linger on the tiiin 
portion of the ebonite plate under the coil B was sufficient to 
destroy the balance. 

This was remedied by strengthening this portion by means 
of a rod of ebonite, which passed up througli the centre of 
the coil and through a slot I, in the upper elxmite plate, and 
was clamped tirmly after the adjustment of the instrument 
by an ebonite thumb-screw H. This, however, increased the 
difficulties of adjustment. When the coils were adjusted to 
silence, then the tightening of the thumb-screw II disturl)ed 



30 



the balance; and if tlie tlninib-screw H was tightened first, 
then the adjustment couhl only be made by a series of jerks, 
on account of fiiction. In practice we found it best to adjust 
the instrument aluiod to silence, and then the tightening «»f the 
thumlt-screw II completed the l)alance. 

This was the form of apparatus at which we had arrived at 
the time of the death <»f President (lartield. 

The difficulty of adjusting the coils led me ultimately to the 
idea of the apparatus shown in Figs. 21, 22, 23, 2-1-, which is 
the most practical form of the instrument yet devised. 



Fig- 21. 



The two exploring 
coils A B (Fig. 21) are 
arranged as shown, in a 
recess turned out in a 
single 1)l()ck of wood C. 
The coils are tempo- 
rarily connected with a 
telephone, battery and 
rheotome in the manner 
shown in Fig. 1, so that 
they maybe adjusted l)y 
hand to form a balance. 
When they have been 
arranged in tlieir posi- 
tion of silence the liol- 
%// /k^^-l low in the block of wood 
' ^ ^ C (Fig. 21) is filled with 

melted paraffine. Upon cooling, the two coils are found im- 
movably fixed in one solid cake, of paraffine. 

As a matter of practice it is found impossible to fix the coils 
in this way exactly in their position of silence ; l»ut by means 
of two other very small coils, D E, (Fig. 22,) of insignificant 
resistance, forming a sort of fine adjustment external to the 
explorer, a perfect balance is easily obtained. In tliis instru- 
ment the swaying of the coils A B pi-oduces no efi'ect upon 
the balance. 

The completed arrangement is shown in plan in Fig. 22, 
and the explorer and l)alancing coils are shown separately in 
perspective in Figs. 23 and 21:. 





^ 


t3* 


p 


(D 


m 








^ 


n 


^, 


o 


Ul 


P 


o 


r+ 




< 


C 


". 


o 


U) 




& 















CD 


o 








-vl 






(D 




o 














00 


, 


CD 


tr 



38 



Fig.25. 




On account of the small size and slight resistance of the bal- 
ancing coils we were enal»le(l to make the adjustable parts of 
the balancer of metal without practical interference witli the 
sensitiveness of the exploring instrument, and this gave us the 
power of making very delicate adjustments of the balancing 

coils. 

We found it advisable, however, 

to avoid placing metal over the 
sensitive area of the coils as had 
been done in the instrument shown 
in Fig. lU. 

In the balancing apparatus 
shown in Fig. 25, (which is the 
most perfect one yet constructed,) 
the lever to which the upper coil 
is attached is made of hard 
rubber. 

In Fig. 26 is shown the most convenient form of case yet 
devised for holding the exploring coils. 

Bv invitation of Dr. Frank 
^^^^^ Hamilton expernnents were 
made at his office in New 
York October 7, 1881, the in- 
struments nsed being those 
shown in Figs. 22, 23, 24. 
As this was the first suc- 
cessful application of the Induction Balance to the discovery 
of the situation of a ball in the body the position of which 
was previously unknown, I may be pardoned for entering some- 
what into detail. 

I shall (juote from the Medical Gazette,'^ of New York, an 
account of the experiments written by one of the witnesses: 

" The First Saccessfal Aj)plicath))\. 

" On Friday, Oct. 7, by invitation, several medical gentle- 
" men,- including the writer, met Prof. Bell at the house of 

1 See Medical Gazette, Oct. 15, 1881, pp. 347-8-49. 

2 " The foUowiug are the names of the medical gentlemen who were ji resent, 
" each one of whom verified personally the results and declared his entire 




39 

" Dr. Frank H. Hamilton, in this city, for tlie purpose of wit- 
" nesting the practical application of lii.s iuipi-oved instrument. 

" The first person sul)jected to experiment was General 
" Calvin E. Pratt, judge of the supreme court of the State of 
"New York, and who is now a resident of Brooklyn. Gene- 
" ral Pratt, at the battle of Gaines' Mills, June, ' 18()2, this 
" being the second day of the famous seven days' retreat across 
" the peninsula, received a ball in his left cheek, which pene- 
" trated through the nares and was lodged in tlie right antrum. 
" Its presence at this time was recognized by his surgical at- 
" tendant. Dr. Damainville, and its exact position has been 
" known from that day until this, it having given rise at times 
" to nnich pain and suffering. 

" General Pratt has been seen by Dr. Hamilton and Dr. 
" Damainville occasionally from that time forward, and they 
" have from time to time urged upon him the necessity of its 
" removal. General Pratt, however, was anxious to know 
" Avhether Prof. Bell's instrument would indicate its presence 
" at the same point as declared hy his surgeons. 

" The results of the experiment were conclusive and entirely 
" satisfactory to General Pratt, the response l)eing heard dis- 
" tinctly, l)ut rather feebly, l)y every person present in the 
" room. The feebleness of the response was supposed to be 
" due to the fact that, owing to its situation and the peculiar 
" form of the instrument containing the induction coils, it was 
" impossil)le to l)ring the centre of its surface very near the 
" site of the l)all, the ball being situated very near the depres- 
" sion at the ala of tiie nose." 

" The next patient was Col. B. F. Clayton, who i-eceived a 
" wound at the l>attle (»f Cedar Mountain, Virginia, Aug. 9, 
" 1862. 

" The missile was supposed to be an Enfield rifie ball, and 
" the wound was supposed to be m(»rtal by the medical director 
" of General Banks' staff and his assistants. The ball passed 
" through the sternal end of the left clavicle, and was supposed 
" to have lodged in the muscles under the superior angle of tlie 
" corresponding scapula. The injui-y was followed by complete 
" paralysis of the left arm, continuing for a period of six months ; 
" and his arm has never yet l)een completely restored to its nor- 
" mal condition. He suffers a great portion of his time from 
" pains in the arm, shoulder, and portions of the back. 

" satisfaction ^Yith every experiment that was made : J. C. HTitchinson. J. 
" G. Johnson, and J. G. Allen, of Brooklyn : Elias Marsh, of Patterson. N. J.; 
" Nathan Bozeman, J. H. Hiiuter. G. Dnrant. F. Delatield. L. Damainville, 
" W. M. Chamberlain, J. H. Girdner, Frank H. Hamilton, and E.J. Bermiug- 
" ham, of New York." 



40 



" Several tsmall frai2;iiient8 of bone escaped through a fistu- 
" hjus orifice formed near the seat of the original wound. 
" About eighteen months later an a! )scess opened on thefi'ont 
of the chest below the fifth rib and to the left of the stenunu. 
Through this sinus his surgeon was al)le to carry a prol^e up- 
wards and backwards towards tlie top of the shoulder several 
inches, and wliich sinus was supposed then to communicate 
with the seat of the l)all on the l)ack. 

" Pleural adhesions were recognized by the medi(;al attend- 
ants as having occurred in the upper part of the left thoi'acic 
cavity. He has 1)een troul)led occasionally ever since the 
injury with cough, expectoration, and violent palpitations of 
the heart. A suspicion has even been entertained that the 
fistulous canal which remained open a peri(jd of eighteen 
months, and then became permanently closed, comnnmicated 
with the bronchial tul)es, l)ut at no time was a suspicion en- 
tertained by liim or his medittal attendants that the ball was 
not lodged in the back and there closely encysted. 
" We are disposed to mention as an evidence of Col. Clay- 
ton's loyalty and faithfulness as a soldier that witliin six 
months of the receipt of the injury, and while the wound was 
still discharging pus and l)lood, he returned to active duty 
witli his regiment ._nd remained in tlie field until the close of 
the w^ar. 

" In the presence of the gentlemen assembled Col. Clayton 
exposed his chest, and Prof. Bell proceeded to move the coils 
across that portion of his back where the ball was supposed 
to 1)6 situated, the colonel indicating the point underneath 
the superior angle of the scapula as that which had been fixed 
upon l)y himself and all the surgeons who had examined him 
as its exact seat. Although being buried underneath the 
scapula, they had not been able to verify their diagnosis l)y 
the sense of touch. Pepeated examinations were made over 
this region witlujut any response both by Prof. Bell and sev- 
eral of the gentlemen who were present. 
" The instrument was then moved in every direction across 
the back and shoulders with the same result. There was an 
evident feeling of disappointment on the part of Prof. Bell 
and all the gentlemen present, for no one entertained a doubt 
up to this moment that the situation of the ball was known 
and correctly stated by Col. Clayton. 

" It was not until the lapse of half an hour, and a thorough 
examination on the part of Prof. Bell to determine if there 
was not some imperfection in the working of tlie apparatus, 
that it was suggested to move the instrument along the front 
of the chest. 



41 



FUj.27. 



'" This was done by Prof. Bell, atid iiiimediiitely lie exclaiiiicd : 
" 'I have found it!' And such was evidently the fact, as was 
" verified by the personal examination throuuh the tek'ph(»ne 
" by every gentleman present. The response when the instrii- 
"• ment was moved over the seat of the ball was loud and dis- 
" tinct, and left no room for douht.'" 

After all the visitors present had had the o])j)oi't imitv of 
verifyin*^' my discovery (d' the sonorous spot on the clie>t of 
Colonel Clayton, experiments were made to determine as accu- 
rately as possible the exact position of the hall. 

Tiie exploring;' instrument (Fig. 23) was first held ovei- that 
part of the chest where the maximum sound was ol»tained. The 
instrument w^as then moved slowly towards the left imtil the 
sound could no longer l)e perceived. The position of the (-en- 
tre of the instrument was noted, and a verti- 
cal line (A !>, Fig. '27) was drawn with ink 
upon the skin through that point. This line 
indicated the l)oun(lary of the sonorous area 
towards the left. The experiment was then 
repeated l)y moving the instrument from the 
point of maxinunn sound towards the light, 
and also upwards and dowmvards, giving us 
tlie four l)oundarv-lines shown in the diagram. (Fig. 27.) 
Tlie liullet was thus located within a s<juare, (-, of about one 
inch. 

"" The exact situation of the ball,'' as described in the Mcd- 
ical (r(izefk\ " was found to be within the thorax. probaI»ly 
" in imnu'iiiate contact witli the iimer surface of the ribs, the 
" point being a little to the left of the sternum, l)etween tlie 
" third and fourth ril)s, and two or three inches above tlu' cic^a- 
" trix on the front of the cliest, where the sinus, long since 
" closed, had evacuated itself, and in a direct line from this 
" cicatrix towards the left shoulder, whicli indicated the line of 
" the track of the original sinus." 

Durinn' uiv absence from Washington and from all conven- 
iences for experimenting personally with Induction balance 
apparatus, I devised a method of verifying the indications of 



43 



the Iii(lu('tii)ii Bahince and of tiscertaiiiiiii;' the exact deptli at 
which a bullet lies beneath the surface. This method was coni- 
nnniicated through Dr. Woodward to the STn-geons in attend- 
ance on President Gartield, and it was made the subject of a 
special paper presented to the French Academy of Sciences 
Nov. 7, 1881. 

This method, although involving extremely slight pain, would 
ordinarilv be used only as a preliminary to an operationfor theex- 
„. ,.„ traction of a bullet. The 

arrangement is shown 
in Fig. 28. A iine needle 
A is connected to one ter- 
minal of a telephone, and 
the other terminal makes 
contact with a plate B, 
preferably of the same 
material as that compos- 
ing the needle. Place 
this metallic plate B 
against the surface of the 
patient's skin and thinist the needle into that portion of the 
body where the bullet is believed to he lodged. When the 
point of the needle makes contact with the surface of the bullet 
C a galvanic battery will be formed naturally within the body, 
the two poles of which are respectively the leaden bullet C 
and the metallic plate B. Under these circumstances a click 
will be heard from tlie telephone each time the bullet is 
touched by the needle. This has been verified by experiments 
upon luillets buried in a joint of meat. The click, though 
feeble, is unmistakable. 

I have no doulitthat this method of exploration alone, without 
the Induction Balance, would prove of great service upon a field 
of battle, where the employment of complicated apparatus is 
impossible. Mr. Thomas Gleason has recently communicated 
to me the particulars of an experiment he witnessed, in the 
course of which this method was tried upon a living subject. 
The surgeon who conducted the experiment was unable to ob- 
tain any response from the Induction Balance employed, al- 




43 

though from certain indications apparent to the sense of tt.iicli 
he believed that the bullet was located in the ])art of tlie body 
submitted to experiment. 

To verify his supposition a needle connected as above (Fig, 28) 
was thrust into contact witli the hard sul)stance perceived. l)ut 
no response was made by the telephf.ne. The surgeon, how- 
ever, believing tliat the bullet had \)vvn found, etherized his 
patient and proceeded with an operation, but <Hscovered, when 
too late, that the bullet was not there. 

Finilier Miulifcat'ionH of Induction Balance. 

I sailed for Europe early in October, 1881, and Imve had no 
opportunity since of continuing my researches until (juite re- 
cently. AVhile I was in Europe, however, Mr. Sunnier Tainter 
devised a new kind of Induction Balance which deserves nien- 




tion here. The results ol)tained with this apparatus in its pres- 
ent form (Fig. 29) are not to he compared with those produced 
by the best instruments described above, but there are undoubt- 
edly great possibilities of future development. 



44 



The inipoi'taiit feature is that the expLiring instnnneiit E 
consists of a ahigle coil, s(j that there is no possil)ility of any 
part of the explorer o-etting out of adjustment. All the ad- 
justments are made upon the stationary part of the apparatus. 
The current of the liattery is divided between two equal cir- 
cuits. One of the primary circuits contains the coil A and 
the exploring coil E, and the other circuit the coil C and 
a rheostat K. Coils A and C are exactly similar; and if the 
resistance introduced at R is equal to the resistance of the ex- 
ploring coil E, an acoustic balance can l)e ol)tained by the ad- 
justment of the secondary coils B I) upon the primaries A C ; 
but if the resistance introduced at 11 is different from that at 
E, Mr. Tainter states that no l»alance is possilde. 

When the apparatus is adjusted to silence tlie a])})roach of 
a l)ullet to the coil E destroys the balance. 

Although the great olqect of the researches that have been 
brought before you to-day has been to find that arrangement 
of Italance wliich will detect a bullet at the greatest distance 
from the coils of the explorer, it must not be forgotten that in 
every case the instrument is more sensitive to the presence of a 
bullet placed inside the exploring coils than to one exterior t<> 
tliem. When, therefoi-e, we seek the location of a bullet in one 
of the limbs, it may he advisable to use an annular coil large 
enough to slip easily over the leg or arm, as the case may be. 

In Mr. Tainter's arrangement tlie exploring coil E (Eig 29) 
might simply be a large ring consisting of a number of convolu- 
tions of thick wire which could be slipped over the limb, or the 

]'ing might consist of two coils, 
forming one side of a Hughes' 
Induction Balance. 

In either case the loudest sound 
will be produced when the bullet is 
in the plane of the ring, and its 
exact location should be deduced 
from three observations. Suppose, 
7' for instance, that with the ring- 

inclined in a particular direction the maximum sound is ob- 
tained when tlie ring occupies the position A B. (Fig. 30.) 



Fiff.30. 




45 

We know tlieii that the l)iillet is in tliat plane. Now, incline 
the ring- in some other direction and explore again. l.ct 
the position of niaxiniuni sound' ])e now C D. We know- 
then that the hnllet is somewhere on the stiviight line formed 
hj the intersection of the planes A B and (M). it is only 
necessary then to make a third ol)servation witli ti)e apj)a- 
ratus so inclined that the plane of the rhig cuts this straio-ht 
line, for instance, the position E F. The point of intersection 
of the three planes G is then the exact j)oint occupied hy the 
l)nllet. 

I sliall conclude this paper l)y the description of an experi- 
ment made in Newport, R. I., a few days ago. The results 
are so unprecedented in my experience that I feel they cannot 
he received as implicitly reliable until the experiments have 
been repeated and veriiied. 




I had arranged u])on a tal)le three coils, (as shown in Fi^-. 
31.) The large tiat primary coil A was connected with a l)at- 
tery of four Bunsen elements and an interrupter, as shown, 
and the two small secondaries of fine wire, !> C, were (con- 
nected with a telephone. 

The secondary B was moved about on the jM-imai-y A until 
a position of silence was obtained. Upon l)ringing a leailen 
bullet near C the Italaiu^e was distiu'bed and a distinct sound 



46 

produced from the teleplione. Thei-e is iiotliing very strang-e 
about this when we know tliat the distance between A and C 
was only 15 centimetres, so that was well within tlie field of 
induction of A ; l)ut what did seem extraordinai'v was that the 
approach of the large steel blade of a penknife to the coil C 
produced no effect ! The iron diaphragm of a hand telephone 
brought close up to the coil C produced no sensible disturb- 
ance of the ])alance, whereas a small disk of lead produced 
quite a marked effect. A disk of copper the size of a tele- 
phone diaphragm also j)i-()(hiced a good effect, Imt the sound 
was not sensibly louder fhaii that due to the suiall leaden disk. 
A diaphragm of '/Anc. occasioned a feeble, l)ut distinct, disturlt- 
ance of the balance. It is mifortunately the case that in all 
the forms of induction l>alance described above lead gives the 
poorest effect of all metals. If people would oidy make their 
l)ullets of silver or iron there would be no ditticulty in tinding 
them in any part of the body I In the apparatus shown in 
Fig. 31, however, it seems (unless s\d)se(pient experiments 
sliould reveal some fallacy) that we have an arrangement which 
is sensitive to lead and not to iron, or, at all events, which is 
more markedly influenced ])y lead than iron. 

It is liardlv necessary to state that when the coil C was re- 
moved to a c()nsideral)le distance fi'om the primai'v A no 
effect was produced by the approach of metal to the coil C. 

I have in this paper l>rouglit Itefore you an outline of a labor 
of hn-e pursued through many anxious days and sleepless nights. 
However imperfect or disappointing may l)e the results so 
far achieved, they are sutflciently encouraging to enalde us to 
look forward with confidence to the attainment of still greater 
perfection. 

I hope to continue these researches in the future ; and cer- 
tainly no man can have a higher incentive to renewed exertion 
than the hope of relieving suffering and saving life. 



APPENDIX 



Note 1.— Another mode of painless exploration suggested itself t<, mv mind 
at tLis time, based npcm the fact that a leaden bnllet is much morr o].a,iuc tn 
light than the substances composing the human body. 

I was aware of the fact that the ingenious M. Trouvee, of Paris, had, l)y 
means of his i)olyscope, produced a light inside a living fish, and was thus 
enabled in the dark to see the anatonncal structure of the fisli as it swam 
about in a vessel of water. 

M. Trouvue had himself shown me a modified form of this apparatus for 
the illumiuatiou of the interior of the human stomach, and I understood him 
to say that when the instrument was used the body of the jiatient could be 
seen in the dark, faintly illuminated, like a Chinese lantern, and tliat the 
extent and h)cation of tumors in the stomach could be detected on account of 
their great oiiacity. 

It occurred to me that leaden bullets were certainly more opa(iue than 
tumors, and that a painless method of exploration might be based u]>on the 
observations of M. Trouvce. 

It would evidently be impracticalile, in the great majority of cases, to 
introduce into the stomach any illuminating apparatus: but if the light of a 
properly protected incandescent platinum spiral, introduced into the stom- 
ach, could produce effects visible from the (mtside— that is, if this feeble 
light could penetrate through the sulistance of one-half of the body—then 
why should not the intense light of an electric arc, or of a lime light, pene- 
trate the whole body frcjm one side to the other so as to jn-oduce siuular 
effects 'i 

The most feasil)le jjlan that occurred to me was to place an electric lanij) 
at one end of a long oj^acpie tube, and to apply the other end closely against 
the skin of the patient. The intericn- of the tube between two plate-glass 
diaphragms could be filled with a saturated solution of alum, or some other 
highly-absorbent transparent sxibstance, so as to obstruct the ])assag(> of heat 
rays. 

Of course, the whole a]iparatus was to lie so arranged that no light from 
the lamp could cscajie into the room to interfere with the exijeriment. 

Under these circumstanci's, the body of the imtient, or at least a ptn'titni of. 
it, should, in a dark room, apiiear self-luminous; and it seemed possible that 
the shadow of an imbedded bullet might be j^rojected upon the skin. The 
track of the biillet might also, perhaps, be discernible as an illuminated 
streak either more or less bright than the surrounding surface. 

These considerations led me to try a number of experiments, which jyroved 
that the method was feasible where the l)ullet was very near the surface of 
the body. On account of the great and irregular refraction of light in pass- 
ing through the tissues of the body, I doubt whether the shadow of a 

47 



48 

deeply-seated small bullet could be distiuguishable upon the skin, unless, 
indeed, a very brilliiint liglit emanating from a single jjoint could be safely 
produced inside the bodj'. 

The following exi^erinients bearing iipon the siibject were made in Boston 
July ()tli, 1881, with the assistance of Mr. Wm. Schuyler Johnson: 

Experiment 1. — Mr. Johiison i^laced in his mouth a glass cylinder contain- 
ing a spiral of jjlatinum wire, which was rendered incandescent by the pass- 
age of an electrical current. He also held in his cheek a small leaden bullet. 

In a dark room the effect was very striking. The cheek appeared semi- 
transparent, and the location of the bullet was detected at a glance by a 
shadowy sjiot uj^on the skin. 

Experiment 2. — A metallic glove button (not more than 4 or 5 mm. in 
diameter) was attached to the glass cylinder by a few turns of black thread 
passed round the cylinder. 

In this case the effect, although not so marked as in the former experiment, 
was quite discernible, and a faint shadowy streak could be seen crossing the 
cheek, caused by the shadow of the Idack thread tied round the cylinder. 

Note 2. — Letter from Mr. (reorge M. Hojykimt, publislud in the JVein York 
Tribune, July 11, 1881. 

LETTERS FROM THE PEOPLE — THE BULLET FLRED BY GUITEAU. 

A suggestion that the Induction Balance be used to diseorer itx jM'xition in the 

President's body. 

To the Editor of the Tribune : 

Sir : The attempt upon President Garfield's life and the present condition 
of the sufferer have called forth the nation's deepest sympathies, and elicited 
very many suggestions as to the methods of promoting his comfort and assur- 
ing his recovery. 

As one crisis after another has passed hope has risen, and the people wait 
with earnest desire for the last danger to pass away. 

The attending and consulting surgeons state that it is impossible tt) predict 
the final result of the shot withoiit locating the ball. 

With all deference to the several methods proposed, I desire to suggest a 
method of ascertaining the i)osition of the missile which will be painless and 
harmless, and which, in my experiments under conditions analagous to those 
under which it might be practised in the present instance, has proved suc- 
cessful. I refer to the use of the Induction Balance— a most delicate elec- 
trical instrument for detecting the presence of metals— a modified form of 
which could be easily applied in this case with a reasonable expectation of 
success. This instrument consists of twi) short glass cylinders, around each 
of which are wound two parallel coils of fine insulated copper wire. 

One coil of each pair is included in a battery circuit, in which there is a 
clock microphone. The other pair is placed in a closed circiut with a receiv- 
ing telephone. The two glass cylinders, with their encircling coils, may be 
widely separated. 

The induction set up in the secondary or telei>hone circuit is balanced by 
the reversal of one of the secondary coils, and so adjusted that the induction 



49 

in one of the secondary coils exactly balances or neutralizes the induction in 
the other, so that when the ear is applied to the receiving telephone no sound 
is heard. 

Now, by placing ever so small a jjiece of metal in one of the glass cylinders, 
the electrical balance is disturbed and the clock on the microphone is heard 
to tick loudly, thus indicating the presence of metal, and the same is true if 
the coil be placed in the vicinity of a piece of metal. 

It occurred to me to try the effect of a lead bullet u^jon the instrument, 
placing it at different distances, and separating it from the coil by insulating 
material. The result exceeded my anticipations, as with a set of coils that 
were by no means sensitive I was able to locate the bullet with the coils raised 
a vertical distance of nearly two inches. With more sensitive apparatus it is 
more than probable that the bullet might be located, even thoiigh distant 
several inches, by passing a jjair of coils over the President's back and abdo- 
men : and by com2iarative tests the depth of the bullet might be ascertained. 

GEOKGE M. HOPKINS. 
Brooklyn, July 10, 1881. 

Note 3. — Letter from Mr. G. M. Hopkins to Private Secretary Brown, en- 
closing printed description of Hughes^ Induction Balance. 

Office of the ScrENTiFic Amekican, No. 37 Park Row, 

New York, July IWi, 1881. 
Mr. J. Stanley Brown, 

Executive Mansion, Washington. D. C: 
My Dear Sir : I send here\\-ith a full description of the Induction Balance 
as promised in my note of yesterday. I -n-ill send the apparatus for trial if 
desired. 

I am certain that the bullet can be located with it if it is not too deeply 
seated. 

Please advise Dr. Bliss. 

Very respectfiallv, 

GEO. M. HOPKINS, 

Of the Scientific Americnn. 

'iioTE 4:.— Letter from Mr. Geo. M. Hopkins to Private Secretary Brown ac- 
companying the Hughes' Induction Balance apparatus he for weirded to the 
Executive Mansion for trial. 

60 Irving Place, July VMh. 1881. 
Mr. J. Stanley Brown : 

Dear Sir : I give below a few suggestions in regard to the use of the In- 
duction Balance sent herewith. 

Yerv respectfully, 

GEO. M. HOPKINS. 

Suggestions : Connect A to A, B to B, &c. , as marked on the \\'ires. Strength 
of current used, 15 or 20 volts. 

A strong current extends the influence. Use the clock interrupter, and 
place a drop of mercury in the vulcanite cup to make connection. 



50 

The coils are now adjusted to "sileuce," but will probably have to be re- 
adjusted on their arrival in Washington ; as a ^^g inch movement of one of 
the coils will throw it out of adjustment, it will be seen that the adjustment 
is a matter of great nicety. Two telephone receivers should be employed, 
and the most acute sense of hearing is required to distinguish the ticking 
when the ball is two inches distant from the coils. 

The shorter instrument is intended for application to the patient should it 
be considered sufficiently sensitive to warrant the exjieriment. 

As a preliminary experiment jiass the Induction Balance over the pocket 
containing coins, keys, &c.; also over buttons, brickies, &c., attached to the 
garments. 

Lead is the poorest of all metals to locate with this instrument. If the 
ball were of iron it could be readily found at a distance of 3 or 4 inches. 

Note 5. — Telegram fn mi Prof. Newomb. 

. Executive Mansion, 
Washington, D. C.,July IStli, 1881. 
To Prof. A. G. Bell, 

Care of (J has. Williams.. 109 Court st., Boston, Mass.: 
Perhaps small core for coil no larger than bullet, with very fine wire, might 
give best effect. Shall telegrajA to Rowland to know best theoretical form. 
Telegraph me or Brown, care Executive Mansion, what train you take. 

S. NEWCOMB. 

Note 6. — Telegram from Prof. John Trowhridge. 

Bar Harbor, Maine, July \&th. 
To Secretary Brown, 

White Home. Washington, D. C, for Prof. Bell: 
Make resistance of secondary coils equal to telephone. Put large number 
of turns of wire on primary and secondary coils. Primary coils long com- 
IDared with width. Put secondary coils around middle of primary coils. 

JOHN TROWBRIDGE. 

Note 7. — Telegram and letter frerm Prof. Rowland to Prof. Newcomb. 

Hunter, N. Y., J^Uy Uth, 1881. 
To Prof. Simon Newcomb, 

Executive Mansion, Washington, I). C: 
Telegram just received. Make cores four inches long, with six layers of 
number twenty wire : diameter an inch and one-half. Make outer coil half 
an inch wide and half an inch thick, of finest wire, and slip over inner coil at 

its end. 

H. A. ROWLAND. 

Letter following above telegreim. 

Hunter, July 14, '81. 
Prof. Newcomb: 

Dear Sir : When your telegram arrived I had gone to the Hotel Kaaters- 
kill, about ten miles from here, to stay over night. The telegram was sent 



51 

back to the office to be sent to me, and my friends thought that I had received 
it ; but the stupid man here simjDly kept it and would not send it, because he 
had no authority to send it further. 

I have telegraphed back a rei^ly. The dimensions should ]irobal>ly be 
about as follows : 



Wire. 



Six: leaders o^J\ro.20xmre . 



-4xruihes ? 



I 



-~ -inch- 
squctre-. 



Of course, the two must be precisely alike, and the iuductiou coefficients 
of one should be made to vary by a screw, which would move one of the sec- 
ondary coils nearer to or further from the end of the primary. 
Yours tnaly, 

HENKY A. EOWLAND. 

p_ s, — For these dimensions a telephone with many turns of fine wire in its 
coil would be best. 



Note 8.~Oom?nunicat/om with Prof. J). E. H)i;ih(S, of London, England. 

(a.) Cablegram to Mr. Freece, Superintendent Postal Telegraph, London, 

England. 

Washington, Jidi/ IWi, 1881. 

To Peeece, 

London : 
Can Hughes suggest form of Induction Balance to locate leaden bullet m 
President ? If so, cable at my expense. GRAHAM BELL. 



52 

(b.) Telegraphic reply to above. 

Whitney, 

WasJn'figto/L, D. C: 
Preece says to Graham Bell, Wasliiugton : "Interesting and hopeful letter 
from Hughes with diagrams sent you to-day." 

W. GREEN, 
Pres. West. Union Telegraph Co. 



(c.) Note from Mr. Preece enclosing letter from Pr(f. Hughes. 

General Post Office, London, England, li» July, 1881. 
My Deae Bell : The enclosed very interesting letter from Hughes will 
enable you to make some experiments, which I trust will result in success. 
Yours, sincerely, 

W. H. PREECE. 

Prof. Alexandee Geaham Bell, 

Washington, D. C. 



(d.) Pr<f. Hughes to Mr. Preece. 

108 Gt. Portland street, W. London, July IHth, 1881. 

Dear Preece: In reply to yours of to-day enclosing telegram from Prof 
Graham Bell, I believe a specially-constructed Induction Balance could be 
made to locate the leaden bullet in President Garfield, provided the ball was 
nearer to one side of his body than the other. 

Suppose we have two flat superposed coils on a single reel, so that these two 
coils form a single one as regard their relative distance ; these ct)ils, if con- 
nected with the usual adjusting coils of my balance, could be reduced to 
silence ; then, on moving these coils near a metallic body, sounds would be 



liBls^i^""^ 




heard. Thus the only difference would be instead of as usual taking the 
metallic body to the coils upon a fixed table, we take the coils to a fixed body 
in which we sujipose metal, such as a bullet, to l)e hid. 



53 



Now, su^jpose we take the coils A and move it over a body with a Imlltt, 
thus: 




If bullet near C, we should hear it when coils ji;st above it ; at E, when the 
coils were below; biat if bullet iu the centre of the body, then we should have 
eqiial or probably no indications. 

All this could be most easily dime and with some results if the bullet had 
been of copi>er or silver, l)ut lead has such a high resistance and gives, con- 
sequently, very feeble tones. 

We can easily hear a coj^per penny at some inches distant from the coils, 
but lead requires that it should not be more than one or two inches distant ; 
consequently, more sensitive coils woiild be required or a larger battery. 

I think the experiment a hopeful one, and above all that the coils are easily 
made, and simple exi^eriments could bo first made to find a bullet in a mass of 
cotton. &c. 

The microphone is invaluable as a probe for l)ullets. I made the first for 
Sir Henry Thomson to find out stone in bladder. Biit it is even more applicable 
to bullets. It consists (^f a simple hammer and anvil microphone adjusted 
ujion the handle of the ordinary i^robe. The instant this jsrobe touches any 
hard substance a loud, sharp click is heard in the telephone. The smallest 
shot can thus be heard, and there is a very distinctive tone between when the 
probe strikes a bone or bullet. This instrument is well known to sui-geons, so 
I need not say more about it. 

If you Avrite to Prof. Bell, please enclose this, as I should be })leased to hear 

of his success. 

Sincerely yoiirs, 



D. E. HUGHES. 



W. H. Pkeece, F. li. S. 



Note '.). — Letter from Mr. OharUs E. Ihicll t» (\>l. Rorkincll. 
Col. Rockwell : 

Dear Sik: Please suggest for me that in an electrical test to locate the bul- 
let it will only be done with certainty l)y obtaining a balance, which can be 
done as follows : When the loiadest tick is obtained by placing the inducing 
coil in the vicinity of the imbedded bullet, theu move another bullet of ecpial 
size towards the other coil of the bridge until a balance is had and no tick is 
audible, when the imbedded Ijullet will be known to be a like distance from 

its respective coil. 

CHAELES E. BUELL, 

Electrical Engineer, Ntin Ilaieii, ('onn. 



54 

Note \().—Notefr<»it Dr. CMchester A. Bell. 

N. Y. Central R. 11., between Syracuse and Buffalo, 

Juhj \Q>th, 1881. 

Dear A. G. B.: If your coils are symmetrically arranged, slumld it not be 
possible to balance the effect of a bullet on one side l)y a bullet placed in a 
corresponding position on the other? 

Probably you have thought of this Ijefore, but, if not, it may be worth a 

three-cent stamp. 

Yours, truly, 

CHICHESTER A. BELL. 

Note \\.—N<>te and telegram from Mr. J. II. C. Watts. 

Balto., July lUt, 1881. 
Prof. A. Graham Bell, 

1221 Conn. Ave., Washington, I). C: 
Am working hard at our problem. Succeeded in reaching full three inches 
last night, but owing, I think, to my battery weakening somewhat, can hardly 
reach so far now. Won't you please advise me how you are getting along, 

and oblige, 

Y'ours, very truly, 

J. H. C. WATTS. 

Telegram. 

Baltimore, Juli/ 2M, 1881. 
Prof. A. G. Bell, 

Washington. D. C: 
Have been unable to obtain satisfactory results since first trial, and prob- 
ably yours is at least as good as mine. 



J. H. C. WATTS. 



Note 12.— Letter to Br. Bliss. 



VoLTA Laboratory, 1221 Connecticut avenue, 

Washington, D. C, Juli/ 23, 1881. 
Dr. Bliss, 

Executive Mansion : 

My Dear Sir : You were kind enough to suggest that preliminary experi- 
ments should be made with the Induction Balance upon the person of Lieu- 
tenant Simpson, whose address you gave me. I accordingly communicated 
with the lieutenant, and he came to my laboratory last night in company 
with Dr. Stanton. 

The new instruments we had hoped to use were not complete, so we had to 
content ourselves with the apparatus you tested the other day. 

Upon passing the coils over the back of the lieutenant, it was found that 
at one spot a feeble sound made its appearance — too feeble, however, to be 
entirely satisfactory as evidence of the presence of a ball. I find that very 
feeble sounds like that heard are easily conjured up by imagination and expec- 
tancy, but the following facts seem to indicate that in this case the sound 



55 

was due to au external cause — probalily tv the presence oi a very deeply-im- 
bedded bullet : 

1. The sound, although it could not always be distinguished, imifonuly 
appeared, -when audible, at the name xpot. 

2. It was heard independently by Mr. Taiuter, Dr. Stanton, and myself at 
the same spot. (If I recollect rightly, the lieutenant himself also located the 
sound, but my father could hear nothing.) 

3. A blindfold test was then made. Mr. Taiuter closed his eyes and turned 
away while the coils were moved over different parts of the lieutenant's back. 
The moment the sonorous spot was covered Mr. Taiuter declared he could 
hear the sound. We are to repeat the experiments with our new instruments 
as soon as they are completed, and I shall report progress. 

Yours, truly, 

ALEXANDER GRAHAM BELL. 



Note 13. — Letter to Dr. Bliss. 

Washington, July '21th. 1881. 
Dr. Bliss: 

My Deak Sie : Permit me to make a few remarks upon the value of the 
indications of the Induction Balance in deterniiniug the location of a lead 
bullet imbedded in the hiiman body. 

Podtive deductions concerning the location of the ball can only he safely 
made from positite indications of its presence. Negative indications may 
mean anything. 

For instance : If we hear a sound from the telephone connected with the 
balance every time the ex^jloring coil is passed over a certain part of the 
body, this may be taken as i^roof ijositive that a metallic mass is to be found 
in the neighborhood of the sonorous spot. If, on the other hand, we fail to 
obtain audible effects, we are not entitled to conclude that the bullet is absent 
from the -p-Aii exi^lored, or that it is imbedded at a greater distance below the 
surface than the penetrating distance of the instrument used, for the bullet 
may be within any part of the area explored and close to the surface without 
affecting the balance if it is flattened, and if it is so located that the plane of 
its face is nearly i^erpendicular to the plane of the face of the exploring coil. 

A few words may not be out of place here concerning the experiment made 
last night u^ion the i^erson of the President. 

Before entering the President's room, I applied the tele^jhouc to my ear, 
and heard a peculiar spluttering sound which it was found impossible to 
extingiiish by any adjustment of the coils. I satisfied myself, however, that 
the arrangement was in a sensitive condition, by holding near it a flattened 
bullet. The hearing distance appeared to be about 4 cm. When the exi^lor- 
ing coil was passed over the back of the President near the spine, no definite 
pulsation of the sound was heard ; but when the coil was first passed over a 
portion of the front part of the abdomen near the right side, I heard at one 
jwint a sharp and sudden reinforcement of the sound. Upon moving the coil 
backwards and forwards a nimdier of times over the same spot, I was unable 
to verify the observation. I should state here that, when a i)erfeft balance is 



56 

not obtained, it is not safe to place reliance iipon a single observation of a 
pulsation in the sound, as a similar eifect might be caused by an accidental 
irregularity in the vibration of the instrument used to interrupt the electrical 
current. 

The sound heard was distinct and well marked, but it would not be safe to 
conclude that it was due to the jDresence of the bullet, unless the effect could 
be reproduced a number of times and always at the same si^ot. 

I think I mentioned to you that it was discovered yesterday morning that 
the application of a tin-foil "condenser" to the Indiiction Balance markedly 
influenced the hearing distance, increasing it iu our experiments by about one 
centimetre. 

A condenser was therefore connected to the arrangement used last night, 
but it has since been found that the condenser was only connected to one side 
of the balance, instead of to both. This mistake is enough to account for the 
difficulty exi^erieuced in adjusting the coils so as to obtain an acoustic bal- 
ance, and for the observed reduction in the hearing distance. 

If it is of imjiortance to locate the bullet at once, I would recommend an 
immediate repetition of the experiment with the condenser properly arranged. 

Whatever other resiilts might be obtained, I feel siire we could, at all 
events, settle immediately whether the sound I heard was due to the presence 
of the bullet or was an accidental phenomenon. 

If it is not imj^ortant to locate the bullet at the jn-eseut time, it might be 
well to postpone a repetition of the experiment, so as to give Mr. Tainter and 
myself more time to improve our api)aratTis. 
Yours, truly, 

ALEXANDER GRAHAM BELL. 



Note U.— Letter to Dr. Bliss. 

VoLTA Labokatoky, 1221 Connecticut avenue, 

W^VSHINGTON, D. C, Juli/ 31, 1881. 
My Dear De. Bliss : I write to let you know that my new form of Induc- 
tion Balance gives brilliant promise of success. The indications with a flat- 
tened bullet are well marked and distinct at a distance of three inches, and 
audible effects can even be distinguished at five inches, but beyond three 
inches silence and the greatest attention are requisite. Effects are produced 
at about two inches, when the bullet is held with its edge towards the instru- 
ment — a position that gave no results with our former apparatiis. 

Altogether I feel very much encouraged. The api^aratus in its present form 
is a very clumsy affair, the surface that would be apiilied to the jierson of the 
President measuring seven inches by four. I hope to reduce the size of the 
apparatus very greatly in a day or two. In the meantime, should any neces- 
sity arise for an experiment upon the President, we have much better chances 
of success than at any previous time. 

Yours, very truly, 

ALEXANDER GRAHAM BELL. 



57 

Note la.— Letter to Br. Blun. 

VoLTA Laboratory, 1221 Connecticut avenue, 
D^. Bliss Washington, D. C, July 31, 1881. 

Executive Mansion : 

Dear Sir: We have made experiments this evening upon the person of 
Private John McGill, an old soldier, who was wounded at the battle of Gaines' 
Mill, in 1862. and who still carries the ball that shot hiui. 

I found no difficulty in finding a sonorous spot in his back, where undoubt- 
edly the bullet lies imbedded. 

Mr. Tainter also located the bullet in the same place. Upon pressing with 
the fingers upon the spot a lump could be felt between two of the ribs. We 
experimented upon this same man yesterday, using a similar form of Induc- 
tion Balance to that we tried upon the person of the President the other dav. 
but could obtain no indications. 

The new form of Induction Balance is so sensitive that a new difficulty is 
introduced by the effects produced by large metallic masses— for instance, 
gas lustres, iron fire-places, &c. 

I think also that the earth's magnetism affects the result. We shall inves- 
tigate these causes of disturbance to-night. 
Yours, sincerely, 

ALEXANDER GRAHAM BELL. 

Note l&.—Report to the surgeons published in the daily papers Aug. 2, 1881. 

Volta Laboratory, 1221 Conn. Ave., 

Washington, D. C, Aug. 1st, 1881. 
To the Surgeons in attendance upon President Garfield : 

Gentlemen : I beg to submit for your information a brief statement of the 
results obtained with the new form of Induction Balance in the experiments 
made this morning for the purpose of locating the bullet in the person of the 
President. The instrument was tested for sensitiveness several times during 
the course of the experiments, and it was found to respond well to the presen- 
tation of a flattened bullet at a distance of about four inches from the coils. 

When the exploring coils were passed over that part of the abdomen where 
a sonorous spot was observed in the experiments made on July 26th a feeble 
tone was perceived, but the effect was audible a considerable distance around 
this spot. The sounds were too feeble to be entirely satisfactory, as I had 
reason to expect from the extreme sensitiveness of the instrument a nnich 
more marked effect. In order to ascertain whether similar sounds might not 
be obtained in other localities I explored the whole right side and back beknv 
the point of entrance of the bullet, but no part gave indications of the jiresence 
of metal, excejat an area of about two inches in diameter, containing within 
it the spot previously found to be sonorous. The experiments were repeated 
by Mr. Tainter, who obtained exactly corresponding results. We are therefore 
justified in concluding that the ball is located Avithin the above-named area. 

In our preliminary exi^eriments we found that a bullet like the one in (pies- 



58 

tion when in its normal shape produced no atidible effect beyond a distance of 
two and a half inches, while the same bullet, flattened and presented with its 
face parallel to the plane of the coils, gave indications iip to a distance of five 
inches. The same flattened bullet, held with its face perpendicular to the 
plane of the coils, produced no sound beyond a distance of one inch. The 
facts show that, in ignorance of the actual shape and mode of presentation of 
the bullet to the exploring instrument, the depth at which the bullet lies be- 
neath the surface cannot be determined from our experiments. 
I am, gentlemen, j'ours truly. 

ALEXANDER GRAHAM BELL. 



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